This invention relates to a pressure flow controller and particularly to such a controller for a vacuum operated flow system having means responsive to abnormal conditions to establish a flow.
In flow systems, the pressure differential for establishing flow may include a downstream vacuum source. A temporary storage means such as a storage tank, a standpipe or the like within which liquid is stored until it reaches a selected level may be incorporated into the system. When such a selected level is reached, a discharge apparatus is actuated to remove liquid generally until a lower limit is established.
A particularly satisfactory two-position liquid level controller for a vacuum operated sewage disposal system and the like is disclosed in U.S. Pat. No. 3,777,778 and in the copending application of Trobaugh et al entitled "Flow System With Pressure Level Responsive Air Admission Control" filed on Oct. 28, 1977 with Ser. No. 846,405. In that fluid system a sensor is mounted upstream of a discharge control valve and is connected to actuate a triggered controller having a fluid relay connected to charge a fluid timing capacitor which, in turn, actuates a fluid switch.
When the output signal from the sensor is received, the vacuum connection to the capacitor is momentarily made and the vacuum established as a reference. The storage device signals the fluid switch which actuates a pilot valve to open the main valve. The sewage flow continues until such time as the main capacitor has totally discharged, at which time the switch converts to an "off" condition, resetting the pilot valve and moving the main valve to a closed condition.
In operation of such vacuum operated systems, a low vacuum condition may be created in the sewer line between the main control valve and the vacuum source by low points in the flow line being filled by sewage and/or by a partial system bogdown or water logging. The sewage or water laying in the low points thus prevents creation of system vacuum and interferes with proper system operation. The system vacuum can be restored by admitting air into the system to force the sewage in such low points forward toward the collection station and clearing of such low points.
The above identified application provides an automatic admission control means for sensing a low system pressure condition and signalling the controller for supplying pressure to the line and thereby positively clearing of the system line and re-establishing proper system pressure.
The particular air admission valve means shown therein includes a diaphragm bleed valve connecting the controller trigger input to a signal pressure. The bleed valve includes a pressure input connected to the vacuum side of the line to establish the trigger signal when the vacuum falls below a selected level. A parallel bleed-type reset valve is connected in parallel with the trigger valve and is actuated by application of valve opening pressure to the main valve to reset the input to the controller.
Although the air admission control produces a satisfactory means of triggering the controller, the inventor has found that undesirable triggering may occur under transient pressure conditions.
Thus, various operating systems may encounter a momentary or transient low vacuum pressure condition as a result of normal operation. Under such conditions of course, the air admission control unit would normally respond to actuate the main valve unit even though the system did not require such action. Further, in a vacuum actuated operated sewage flow system, a number of valve assemblies may be operating at essentially the same static head and as a result of corresponding operations generate a momentary low vacuum condition from the main vacuum supply or source. Such a condition would, of course, be transmitted to other units and result in the further actuation of other valve subassemblies even though, in fact, such branches were operating in accordance with designed characteristics and there was no need for such additional controlled valve operation. The unnecessary operation consumes energy as well as requiring component operation without any functional benefit.